1. Field of the Invention
The present invention relates to a light source unit, and more specifically, to a light source unit incorporating a light emitting device and an optical device, for use in a laser beam printer, a copying apparatus, a laser facsimile apparatus, a laser composing apparatus, a bar code reader and a sensor.
2. Description of the Prior Art
Light source units having semiconductor lasers are used as light emitting sources for various apparatuses such as the above-mentioned ones. For example, in an image forming apparatus such as a laser beam printer, a copying apparatus and a facsimile apparatus, a light source unit is used as an apparatus for irradiating a laser beam for forming images such as letters and pictures on an electrophotographic drum at a high speed. In a laser composing apparatus, it is used as an apparatus for irradiating a laser beam for making master film for printing. In a bar code reader and various types of sensors, it is used as an apparatus for irradiating a laser beam for obtaining information by means of reflected beams from a bar code and an object.
Typically, a light source unit used as a light emitting source for various apparatuses such as the above-mentioned ones has a structure where one, or two or more pairs of semiconductor laser and collimator lens are fixed to a fixing member. FIG. 1 shows a part of a typical multi-channel light source unit 3. Although the light source unit 3 is of a structure where a plurality of bar bodies 34 are fixed to a base board 5, in FIG. 1, only one eight-channel bar body 34 is shown which is fixed to the base board 5 by screws 35 at both ends.
In the bar body 34, as shown in the plan view of FIG. 2 (cross-sectional structure is partly shown), eight holes H1, and eight holes H2 arranged opposite to the holes H1 with a groove therebetween are formed. Into each of the holes H1, a semiconductor laser 40 is inserted. Into each of the holes H2, a lens barrel 20 in which a lens 15 is fixed is inserted.
The semiconductor laser 40 and the lens barrel 20 are typically fixed to the bar body 34 by YAG laser welding or an adhesive. In the light source unit 3 of FIG. 1, the fixing is performed by YAG laser welding. Each lens barrel 20 is, as shown in FIGS. 1 and 2, YAG laser-welded to the bar body 34 at four points P.sub.1 to P.sub.4. Regarding the semiconductor lasers 40, the welding is performed to four points Q.sub.1 to Q.sub.4 (Q.sub.2 and Q.sub.4 are omitted) as shown in FIG. 2. YAG laser welding is performed by irradiating a YAG laser beam from a YAG laser irradiating nozzle unit to the border between the bar body 34 and the semiconductor laser 40.
The fixing by an adhesive will be described with reference to FIGS. 1 and 2. In order to fix the lens barrel 20, a hole is formed in a part of the bar body 34 in a vertical direction toward the lens barrel 20 inserted into the hole H2, and an adhesive is filled into the hole. In order to fix the semiconductor laser 40, the adhesive is applied on the welding points Q.sub.1 to Q.sub.4 shown in FIG. 2. As the adhesive, an instantaneous adhesive (e.g. one made of cyanoacrylate) or an ultraviolet setting adhesive (e.g. one made of epoxy acrylate) or a two-component room temperature setting adhesive (e.g. one made of epoxy resin) or a two-component thermosetting adhesive (e.g. one made of epoxy resin) is used.
In the case where the fixing is performed by YAG laser welding, the lens barrel 20 or the semiconductor laser 40 is instantaneously fixed under a condition where it is accurately positioned, and the strengths at the welding points are high. However, since the YAG laser welding is a spot welding performed to a small portion into which a laser spot can go, the welded portions are fragile and have a lower degree of tolerance for a shock. For example, the lens barrel 20 inserted into the hole H2 as shown in FIG. 2 is rotation-decentered (at an angle .theta. of decentering) by a shock within a clearance between the bar body 34 and the lens barrel 20 so that the optical axis of the lens 15 shifts from the position of an optical axis AX1 (vertical to a reference surface S.sub.0) to the position of an optical axis AX2.
In the case where the fixing is performed by an adhesive, even though the lens barrel and the semiconductor laser have been positioned, it is necessary to do something to maintain the positioned condition until the adhesive sets while monitoring the laser beam irradiated through the lens 20 from the semiconductor laser 40. In the case where a two-component adhesive is used, although its adhesive strength is high, its setting time is long; it takes several minutes (several tens of minutes to several hours in the case of the two-component thermosetting adhesive) for the adhesive to set. Accordingly, it takes a long time to fix each, so that the cycle time of manufacturing the light source units per a fixing apparatus is long. In the case where the ultraviolet setting adhesive is used, although its setting time is short and its adhesive strength is high, only a small portion into which ultraviolet rays can go can be fixed. For this reason, with only this adhesive agent, it is difficult to make fixing to desired positions. In the case where the instantaneous adhesive is used, although its setting time is short, its adhesive strength is low and decreases with time, and the lens may be clouded according to the application position of the instantaneous adhesive.